1. Field of the Invention
The present invention relates to prosthetic heart valves. More particularly, the present invention is directed to heart valves of the type including sewing ring to be permanently mounted in the heart and a removable valve member mounted in the sewing ring.
2. Description of the Prior Art
Typical prior art prosthetic heart valves are essentially permanently installed. Both mechanical valves and tissue valves are sutured into place. These valves are further fixed in place by ingrowth of tissue on the perimeter.
Of course it is not possible to design a prosthetic heart valve that will last forever. All valves have some natural life. At the end of the life cycle, it is appropriate to remove the prosthetic valve and replace it with a successor valve. Additionally, children require replacement of valves because of changes in their heart size as they grow.
The replacement of the heart valve can be difficult. Because of tissue ingrowth, the surgery required to remove the implanted heart valve and implant the successive replacement can be more complex than the original implantation operation.
Attempts have been made to ease this replacement by providing heart valves with replaceable elements. For example, U.S. Pat. No. 3,997,923 to Possis discloses one attempt to solve this problem by having a removable valve member snapped into a permanent sewing ring. This type of attachment mechanism is susceptible to overgrowth by tissue, which impedes removal. An improvement on this mechanism is shown in U.S. Pat. No. 4,680,031 to the present inventor. In that case, a valve member was removably threaded onto a permanent sewing ring.
A further goal of prosthetic heart valves is to increase blood flow through the valve. A valve which offers the least obstruction to the flow of blood maximizes cardiac output. Previous sewing rings have considerably narrowed the opening through which blood flows. It is desirable to cover as little possible of the natural opening of the heart with the sewing ring and valve mechanism.
A valve according to the present invention improves on the prior art by providing a more easily removable valve member, as well as maximizing the open bore of the heart valve.